1. Field of the Invention
The present invention relates to a test pattern signal generator and generation method, color measurement system and display device suitable for testing the display of colors represented, for example, by the xvYCC color gamut.
2. Description of the Related Art
Today, some among existing display devices designed to receive and display video data offer improved color representation capability. That is, the color representation capability of video data handled by existing display devices basically assumes the use of a CRT (Cathode Ray Tube) as display means. A color range representable by primary color data, i.e., R, G and B data, has been set by bearing in mind the color range representable by a CRT.
As for display means incorporating a display device, on the other hand, new types have come along which provide a wider color representation range than a CRT. In the case of a liquid crystal display, for example, the color representation range is determined by the characteristic of the light source used as its backlight. This makes it relatively easier to expand the color representation range than with a CRT.
A standard called “xvYCC” has been developed recently as a standard for video data (moving image data) handled by such display devices with a wider color representation range. By processing video data represented in compliance with “xvYCC,” pictures with a wider color representation range can be displayed. It should be noted that RGB data in the existing color representation range will be referred to as the “sRGB signal” in the description given below.
Here, a description will be given of the color range representable by a television set, computer monitor and so on with reference to FIGS. 9 and 10.
FIG. 9 is a u′v′ chromaticity diagram in which a three-dimensional object (color space) is projected in a display device capable of receiving and displaying RGB data, namely, primary color data. The horizontal axis represents “u′” and the vertical axis “v′.” In FIG. 9 illustrated as a u′v′ chromaticity diagram, the range of colors typifying Nature is shown as the outer fan shape. In FIG. 9, the triangular area enclosed by three points Rs, Gs and Bs, for example, is the color gamut which can be represented by the RGB data used for the existing video signal. If in analog form, each color inside the triangle can be uniquely determined by assigning a value in the range of 0 to 1 as each of the three primary color values, namely, RGB values. The color gamut which can be displayed is determined by which RGB values are assigned. One among such color gamut standards is the sRGB standard. A value represented in the range of 0 to 1 for an analog signal is given, for example, by a value quantized with eight bits for a digital signal.
Because of the characteristic of phosphors of CRTs used as display means, the vertices (chromaticity points of three primary colors) Rs, Gs and Bs of the sRGB standard as shown in FIG. 9 used to match the three primary color points which can be represented by a television set. However, with an increasing number of non-CRT television sets available today such as FPD (Flat Panel Display) and projection type television sets, the color gamut reproducible by a television set has expanded beyond that defined by the SRGB standard (also referred to as the “normal color gamut”). This has made it possible to reproduce a wider color gamut (also referred to as the “wide color gamut”). An example of a color gamut enclosed within a dashed line by vertices Rf, Gf and Bf in FIG. 9 shows the color gamut which can be displayed when video data is configured as an xvYCC signal. The respective points in FIG. 9 indicate the actual chromaticity levels. As is clear from FIG. 9, there are, in the image, a significant number of colors which lie outside the color gamut representable by an sRGB signal. These colors lie in the color gamut representable by an xvYCC signal.
FIG. 10 is a view illustrating the relationship in color gamut between the xvYCC and sRGB signals. The vertical axis represents a brightness signal Y, and the horizontal axis color difference signals Cb and Cr. According to the xvYCC standard, the xvYCC signal employs the same primary color points as the sRGB signal and represents a color with the brightness signal Y and the two color difference signals Cb and Cr as illustrated in FIG. 10, thus encompassing the sRGB color gamut. As illustrated in the same figure, the sRGB color gamut is shown in the form of a rhombus, with an expanded xvYCC color gamut provided around the rhombus.
Japanese Patent Laid-Open No. 2006-33575 describes a signal processing device capable of providing a signal which can represent colors in a color gamut wider than as defined by a predetermined standard and which can be handled by a device compliant with a predetermined standard.